(1) Field of the Invention
This invention relates to a transfer sheet and a process for the preparation thereof. More particularly, the invention relates to a transfer sheet for electrostatically transferring an electrically conductive or electrically semi-conductive toner in electrostatic photography or electrostatic printing.
(2) Description of the Prior Arts
As one of dry developers (toners) for developing electrostatic latent images formed by electrostatic photography or the like, a so-called electroconductive or semi-conductive magnetic toner capable of performing development without the aid of a particular carrier is known. As the toner of this type, there have heretofore been used toners formed by dispersing powder of a magnetic material such as triiron tetroxide, if necessary with a conducting agent such as carbon black, into a binder resin and molding the dispersion into granules. As means for improving the electric conductivity in these toners, there have ordinarily been adopted a method in which the amount of the conducting agent incorporated in the magnetic material-binder resin dispersion is increased and a method in which the conducting agent is embedded in the above-mentioned toner particles. By adopting these methods, toner particles are provided with such property that they can be magnetically attracted, and improved electric conductivity is imparted to surfaces of toner particles.
These magnetic toners have an advantage that sharp and clear toner images having a much reduced edge effect can be obtained according to the magnetic brush development method even without use of a magnetic carrier or the like. However, they have a defect that if toner images formed on photosensitive layers for electrostatic photography or electrostatic printing, such as photoconductive layers, are transferred onto copy papers, contours of the transferred images become obscure and no sharp images can be obtained.